The line transfer type of CCD imager has an image register comprising a parallel array of charge transfer channels arranged for charge transfer in a direction parallel to the direction of scanning of an image projected onto the array. During each field scanning interval, each charge transfer channel may be successively selected for being read out, presuming no field-to-field line interlace is used. The selected charge transfer channel receives a dynamic forward clocking signal to operate it as a CCD shift register, while the other charge transfer channels receive a static clocking signal. Every charge transfer channel receives static clocking signal for its respective image integration interval, which lasts for one frame time prior to the selection of that channel for read out. This static clocking signal establishes an alternating succession of potential energy barriers and wells in the charge transfer channel during its respective image integration interval, and charge carriers generated by photoconversion in the charge transfer channel and the underlying bulk semiconductor accumulate in the wells to form charge packets. The amplitude of each charge packet is representative of the intensity of an image element, or pixel, associated with the potential energy well in which the charge packet is accumulated.
The selected charge transfer channel is read out through a CCD output register to charge sensing stage, which senses the amplitudes of the charge packets sequentially read out from the dynamically clocked charge transfer channel. Typically, this charge sensing stage is an electrometer comprising an insulated-gate field effect transistor having its gate electrode connected to a floating diffusion in the output of the CCD multiplexer and otherwise being connected as a source- or drain-follower. The CCD output register may be a CCD shift register, having its charge transfer channel at right angle to the charge transfer channels in the image register. In such case, the successive charge transfer stages of the output register can be successively side-loaded with a successive line of charge packets from a respective one of the image register charge transfer channels. The shift register output port supplies to the charge sensing stage, in sequence, the charge packets from each charge transfer channel in the image register. Alternatively, the CCD output register may be a "charge funnel", a charge transfer channel wide enough at its input port to connect to the parallelly arranged output ports of all the charge transfer channels in the image register, and narrow enough at its own output port to supply to a small charge sensing stage charge packets of appreciable amplitude variation responsive to variation in radiant energy image intensity. Other alternative CCD multiplexers each comprise a plurality of charge funnels with input ports in parallel, each connected to the parallelled output ports of a band of image register charge transfer channels. The output ports of the charge funnels in certain of these CCD multiplexers go to separate charge sensing stages. The output ports of the charge funnels in certain others of these CCD multiplexers are connected by respective charge transfer channels to the input ports of a charge merging stage, the output port of which subsequently supplies charge packets to a charge sensing stage.
A problem that plagues line transfer type CCD imagers is the appearance of one or two line artifacts in the television picture constructed from the video signal originating from the image. Each line artifact is caused by electrostatic coupling of the forward clocking signal being selectively applied to one or two charge transfer channels in the image register, which electrostatic coupling is to the charge sensing stage via shared capacitance to the underlying substrate. The starting or stopping of such forward clocking signal affects the sensed charge to cause an electrical disturbance or glitch in the scan line. The glitches in successive scan lines form, in the aggregate, a line artifact. If the forward clocking signals of successive line scans start and stop simultaneously--i.e., if each charge transfer channel in the image register is clocked for a full line interval--a single line artifact will appear in the television picture. Clocking the charge transfer channels in the image register for a shorter time--i.e., just during line trace interval--may result in two line artifacts appearing in the television picture. The line artifacts are normal to the direction of line scan in line-transfer CCD imagers using charge-funnel CCD multiplexer circuitry to connect the image register to their charge sensing stages. The line artifacts are skewed in line-transfer CCD imagers using side-loaded CCD shift registers with charge transfer channels at right angles to those in their image registers for connecting their image registers to their charge sensing stages.